Additive manufacturing systems and methods

ABSTRACT

Aspects described herein relate to additive manufacturing systems and related methods. An additive manufacturing system may include two or more laser energy sources and associated optical fibers. An optics assembly may be constructed and arranged to form a rectangular laser energy pixel associated with each laser energy source. Each pixel may have a substantially uniform power density, and the pixels may be arranged to form a linear array of laser energy pixels on a build surface with no spacing between the pixels. Exposure of a portion of a layer of material on the build surface to the linear array of laser energy pixels may melt the portion of the layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 15/940,315, filed on Mar. 29, 2018, the disclosure of which isincorporated herein by reference in its entirety.

FIELD

Disclosed embodiments are related to systems and methods for additivemanufacturing.

BACKGROUND

Many methods of metal additive manufacturing are currently available inthe market. The methods can be separated by source of material (powder,wire, film etc.) and form of energy addition to obtain melting/bonding(laser melting, e-beam melting, welding arc, sintering etc.). Theresolution, accuracy and obtainable feature size of the end part for agiven process is based on the initial material form and the ability tocontrol the energy placement for metal fusion. The effective rate of agiven process is typically limited by the ability to delivery energyinto the build surface in a controlled manner.

In a selective laser melting process for metal additive manufacturing, alaser spot is typically scanned over a thin layer of metal powder. Themetal powder that is scanned with the laser spot is melted and fusedinto a solid metal structure. Once a layer is completed, the structureis indexed, a new layer of metal powder is laid down and the process isrepeated. If an area is scanned with the laser spot on the new layerthat is above a previous scanned area on the prior layer, the powder ismelted and fused onto the solid material from the prior layer. Thisprocess can be repeated many times in order to build up a 3-dimensionalshape of almost any form.

SUMMARY

In one embodiment, an additive manufacturing system comprises a buildsurface, two or more laser energy sources, and two or more opticalfibers. Each optical fiber is configured to transmit laser energy from afirst end coupled to an associated laser energy source of the two ormore laser energy sources and out of a second end, and the second endsof the two or more optical fibers are arranged along a line. Theadditive manufacturing system further comprises an optics assemblyconstructed and arranged to shape the laser energy output from eachoptical fiber to form a rectangular laser energy pixel associated witheach laser energy source. Each rectangular laser energy pixel has asubstantially uniform power density, the rectangular laser energy pixelsare arranged to form a linear array of laser energy pixels on the buildsurface with no spacing between adjacent laser energy pixels, andexposure of a layer of material on the build surface to the linear arrayof laser energy pixels melts at least a portion of the layer ofmaterial.

In another embodiment, a method for additive manufacturing comprisesexposing a layer of material on a build surface to a linear array oflaser energy pixels. Each laser energy pixel has a rectangular shape anda substantially uniform power density, and wherein there is no spacingbetween adjacent laser energy pixels. The method further comprisesmelting a portion of the layer of material due to exposure of theportion to the linear array of laser energy pixels.

It should be appreciated that the foregoing concepts, and additionalconcepts discussed below, may be arranged in any suitable combination,as the present disclosure is not limited in this respect. Further, otheradvantages and novel features of the present disclosure will becomeapparent from the following detailed description of various non-limitingembodiments when considered in conjunction with the accompanyingfigures.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures may be represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a schematic representation of a round beam with a Gaussianpower density;

FIG. 2 is a schematic representation showing the power density of twoadjacent round beams having Gaussian power densities;

FIG. 3 is a schematic representation of the power densities at differentpositions of round beams having Gaussian power densities;

FIG. 4 is a schematic representation of a rectangular beam with auniform power density;

FIG. 5 is a is a schematic representation of the power densities atdifferent positions of rectangular beams having uniform power densities;

FIGS. 6-7 depict schematic illustrations of the incident energy profilesof a linear array of rectangular pixels having uniform power densities;

FIG. 8-9 depict schematic illustrations of the incident energy profilesof a linear array of round pixels having Gaussian power densities;

FIG. 10 depicts schematic representations of power densities of linearpixel arrays, according to some embodiments;

FIG. 11 depicts schematic representations of power densities of linearpixel arrays and fixed spot arrays;

FIG. 12 depicts schematic representations of power density outputs of alinear pixel array, according to some embodiments;

FIG. 13 depicts schematic representations of power density outputs of alinear pixel array, according to some embodiments;

FIG. 14 is a schematic representation of a linear pixel array at a focalpoint;

FIG. 15 is a schematic representation of a linear pixel array away froma focal point;

FIG. 16 is a schematic representation of a pattern of pixels produced byrotationally misaligned square fibers;

FIG. 17-18 depict a schematic representation of rectangular beamprofiles shaped from round beam profiles, according to some embodiments;

FIG. 19 is a schematic representation of one embodiment of an additivemanufacturing system;

FIG. 20 is a schematic representation of one embodiment of an opticsassembly;

FIG. 21 is a schematic representation of one embodiment of a fibermount;

FIG. 22 is schematic representation of one embodiment of a lens array;

FIG. 23 is schematic representation of another embodiment of an opticsassembly;

FIG. 24 is schematic representation of one embodiment of one embodimentof an additive manufacturing system including a galvanometer;

FIG. 25 is schematic representation of one embodiment of one embodimentof an additive manufacturing system including a fixed mirror assembly;

FIG. 26 is a schematic representation of a linear pixel array formed ona powder bed surface, according to some embodiments;

FIG. 27 is a schematic representation of one embodiment of an additivemanufacturing system; and

FIG. 28 is a schematic representation of another embodiment of anadditive manufacturing system.

DETAILED DESCRIPTION

The inventors have recognized and appreciated that the thickness of apowder layer, the size of a laser spot, and the accuracy of laser spotmotion may all combine to influence the dimensional precision andaccuracy of the final part produced by a selective laser meltingprocess. The size and power of the laser spot also may influence therate limit of a given machine process. For example, for a given laserspot size, there is a minimum spot power to enable melting of the powderlayer. Laser powers below this point cannot deliver sufficient energy tomelt and fuse the powder under the laser spot, even if the laser spot isstationary on the powder surface. This minimum energy level is dependenton the material (e.g., the type of metal powder), the thermalcharacteristics of the powder bed, and the absorption characteristics ofthe powder surface with the given laser wavelength. If the laser spot isthen scanned over the powder surface, this minimum laser power has toincrease such that at the scanning velocity, the laser beam can stilldelivery sufficient energy to the powder to melt and fuse the powderduring the time period while a given point is under the laser beam spotprofile. The higher the scanning speed, the higher the minimum powerrequired to maintain a continuous melt pool under the scanning spot.

Additionally, the inventors have appreciated that there is a limit tohow much energy can be delivered under a given laser spot size. Theincident laser energy is typically absorbed over a very narrow layer onthe surface of the powder. This energy is converted to thermal energy inthis thin layer and then conduction and convection allow this absorbedenergy to diffuse further down into the powder layer. Conduction islimited by the fine contact points between the individual powderparticles, and convection occurs through the gaps between the particles.If too much energy is incident on the layer surface, then the energycannot diffuse into the full powder layer fast enough and the powdersurface temperature will reach sufficiently high temperatures tovaporize parts of the metal powder surface. This rapid vaporization atthe layer surface will cause powder particles to be ejected from thepowder surface.

While the high incident energy can cause surface vaporization on thepowder surface, it can also cause vaporization of the metal in a meltpool. The melt pool is the volume of molten metal produced by the laserheating of the metal powder while the laser spot is scanned over thepowder surface. The melt pool may also be described as the volume ofmetal powder after it is melted and before the molten metal coolssufficiently to become a solid again. If some of the metal from the meltpool is vaporized due to excessive energy from the laser spot, the rapidexpansion of the metal during the vaporization process can cause moltenmetal to be ejected from the melt pool. These ejected particles candeform the powder surface in areas yet to be scanned, thus causingfurther melt pool instabilities due to non-uniform surfaces.

Additionally, ejected particles of molten metal may be prone to formingoxides and/or other compounds due to their high surface area, elevatedtemperature, and exposure to surrounding gas during the ejectionprocess. These particles may end up in an area that is scanned andmelted during the continued scan process, and these particles caninfluence the microstructure and mechanical properties of the finalpart.

If the incident laser spot energy is too high and the scan speed isincreased to compensate in order reduce the resulting metal vaporizationissues noted above, the thermal energy may not be able to propagatesufficiently fast into the powder layer to fully melt and fuse all themetal powder. Accordingly, the final part will then contain voids ofunmelted metal powder, which may compromise the properties of the finalpart.

In some instances, the above noted issues can be addressed by reducingthe powder layer thickness to ensure full melting of all metal powderfor a given laser spot energy and scan velocity. However, such anapproach reduces the effective rate of the process as a larger number ofthinner layers are required to build up a given part. Also, there is alimit to the layer thickness as the powder layer thickness cannot beless than the average powder particle size (typically in the 15-45 μmrange).

Another issue arises as the laser spot power and velocities increase. Ifthe incident power and scanning velocity are increased sufficientlywhile still being able to ensure full melting of all metal powder underthe scan track, then the melt pool may still become unstable. Ratherthan producing a continuous melt pool that subsequently cools into acontinuous solid metal track, the melt pool becomes unstable and startsto break into individual molten drops that then cool into disconnectedballs on the surface of the processed area. This effect, sometimesreferred to as “balling,” is a mechanism of forming disconnecteddroplets due to the Rayleigh instability. This instability is observedonce the length to width ratio of the melt pool reaches a certaincritical value. High surface tension gradients can then lead to theformation of voids in the tail of the melt pool. The length to widthratio increases as the melt pool length grows far more rapidly withincreased laser spot scanning speed than the width of the melt pool .Further factors that contribute to this melt pool instability effect arethe specific local arrangement of powder particles, wetting, Marangoniflow and gravity.

In addition to the above, another possible method to increase the rateof a laser-based powder bed fusion/melting process is to increase thespot size. As the spot size increases, the average power density of thespot can remain constant while the total spot power increases, therebyincreasing the effective machine rate. However, the inventors haverecognized that this ability to increase the spot size is limited as ata certain size, the added power results in metal vaporization ratherthan an increased net effective powder processing rate. Also, as thespot size increases, the spatial resolution of the final finished partdecreases. Once the feature size resolution decreases sufficiently, thebenefits of the selective laser melting process disappear as theresulting part will require extensive post machining and processing toobtain a final desired and useful state.

In view of the foregoing, selective laser melting processes in currentmachines are bound by the physical limits of the process. Higher netprocessing rates are not possible while maintaining high quality processconditions. One approach to attempt to address these limits has been toadd multiple laser beams to a single machine, with the beams scannedfully independently using rotating mirrors. For example, machines withtwo or even four beams are available with total powers in the 2-4 kWrange. This approach can allow a higher effective machine rate byincreasing the number of beam spots; however, each spot is still boundby the energy limits outlined above. Moreover, the positional accuracybetween each spot location on the powder layer can make multi spotprocessing of a single point challenging without reducing part accuracyand resolution.

Multi-spot laser systems can have fully independent laser spot controlwhich can be useful for producing multiple independent parts in a singlepowder bed, but the effective rate for each part/spot combination isstill limited by the process power combinations. Using multipleindependent spots on a single part is also possible, but then thelocation accuracy between the spots becomes very important and also verydifficult to control. Part accuracy and resolution may be reduced andcare must be taken to avoid interference between the beams and the beampositioning mechanics. As machine sizes increase to accommodate largerbuild volumes, maintaining positional accuracy between multipleindependent spots becomes even more difficult.

Multi spot lasers systems can also be built with the final deliveryoptics fixed relative to each other. While this approach may aid inresolving the issue of positional accuracy between the spot locations,due to the size of the delivery optics, the layout of the spot locationmay not be optimal. For example, in order to keep the output spotslocated close together, the size of the delivery optics forces them tobe placed significantly further apart than the spot size. In someinstances, the beams can be brought together by placing the optics atangles to each other such that the beams converge either at the incidentareas on the powder surface or at another point prior to a finalreflecting mirror or galvo-scanner assembly. An issue with thisapproach, though, is that the angled incidence of the multiple spotscauses different melt behavior under each laser spot. Different incidentangles also limit how close each spot can be placed and maintained nextto each adjacent spot. In order to get a uniform melt front from twoadjacent round spots, the energy density within each spot has to beuniform, which can be very difficult to achieve with different incidentangles and with separate delivery optics. For this reason, fixedrelative position multi-spot laser systems are typically configured tooperate with individual discrete spots that each generate separate meltpools. The scanning pattern is then designed to incrementally step overthe gaps between the spots on successive scan passes. Moreover, theissue with placing multiple fixed optics heads next to each other putspractical limits on the number of laser units that can be employed atone time with this approach, and thus fixed independent laser opticshead systems are typically limited to four to five individual laserspots.

Yet another approach used to try and address the above-noted powerdensity limitations for single or multi-spot selective melting systemsis to scan a spot very quickly back and forth along a linear path togenerate a heated area that on average takes on the shape of a line.Even with very fast scan speeds, however, the resulting average lineshape is still limited in power input by the thermal transfercharacteristics of the powdered metal layer, as discussed above. Forexample, too much power still leads to metal vaporization and melt poolinstability.

In view of the above, the inventors have recognized and appreciatednumerous benefits associated with selective laser melting systems thatutilize a line shaped incident energy source. For example, such systemsmay provide increased effective material processing rates compared tothe above described approaches. In some embodiments, the instantaneousshape of the incident energy is a line with one dimension (e.g., alength of the line) greater than a second dimension (e.g., a width ofthe line). The power density profile across and along the line may becapable of being controlled to be substantially uniform and the line maybe able to be scanned in at least two directions with the primaryscanning direction perpendicular to the long dimension of the line. Insome embodiments, the power density profile of the line can be modulatedin time.

Embodiments described herein address many of the above-described issueswith increasing the effective laser power delivery limits describedwhile maintaining part resolution and accuracy even over larger buildvolumes in powder-bed metal additive manufacturing. The systems andmethods described herein can deliver an arbitrarily large amount oflaser power to the build surface in a controllable profile that can bescanned as a single entity. In some embodiments, the ideal shape of thisincident laser power is a line with a long dimension and a shortdimension where the primary scanning direction is perpendicular to thelong direction of the line. The power density over the long direction ofthe line can be made substantially uniform.

According to some aspects, a line of incident laser energy consists ofmultiple individual laser energy pixels arranged adjacent to each otherthat can have their respective power levels individually controlled.Each laser energy pixel may be turned on or turned off independently andthe power of each pixel can be independently controlled. The powerdensity across any single pixel can be substantially uniform such thatthe pixel has a top hat energy profile when that pixel is turned on. Insome embodiments, the power densities of two adjacent pixel may producea uniform power density across the long length of the resulting linewhen both pixels are turned on and set to the same power densities.

Because the resulting pixel-based line is scanned primarilyperpendicular to the long axis of the line, the forward velocities andpixel power densities are still bound by approximately the same powerand velocity limits as traditional single spot laser selective meltingprocesses. However, because there are multiple spots directly adjacentto each other, the effective process rate can be approximately N timesthe single pixel rate, where N is the number of available pixels. Also,because each pixel can be individually turned on or off, the effectivepart resolution and accuracy remains comparable to a single spot system.The system can be operated as a single spot system by only turning on asingle pixel, but then the effective system rate will be substantiallythe same as a single spot system.

In some embodiments, an additive manufacturing system includes anoptical path arranged within an optics assembly (e.g., an optics box) togenerate the line comprising a set of lenses arranged in series.Alternatively or additionally, a mirror or multiple mirrors can be addedto the beam path for beam turning or folding, and/or a galvo-scanner canbe added to the beam path for one-axis powder bed scanning.

According to some aspects, laser energy for each laser energy pixel isgenerated by an independently controllable laser energy source and isdelivered to the optics assembly through an individual optical fiberassociated with each laser energy source. In some instances, eachindividual optical fiber may include fiber segments spliced together toform a single optical fiber. Alternatively or additionally, a singleoptical fiber path may be generated by using an optical connector tocouple the ends of two fibers together. All of the optical fibers fromthe multiple (e.g., two or more) independent laser energy sources arerouted to the optics assembly. Within the optics assembly, the ends ofthe optical fibers are received in a mounting fixture (e.g., a fiberholder) that ensures the ends of the optical fibers are parallel andaligned. The ends of the multiple fiber optic cables may be cut andpolished to ensure a clear and uniform optical path at the exit fromeach optical fiber. The ends of the multiple fiber optic cables may alsobe coated with an anti-reflected coating. From these fiber terminations,all the individual laser beams pass through a single set of opticallenses and mirrors within the optics assembly. This arrangement keepsthe optical path of all laser energy sources identical and ensures theindividual pixels from the individual laser energy sources to remainadjacent while keeping the size of the optical system to a minimum.

With all optics following the same optical path through the same lensarrays, the resulting laser energy line maintains its shape and may bereflected by single mirror assemblies and scanned using a single axisgalvo-scanner mounted mirror. In this manner, an arbitrarily largenumber of laser systems can be combined into a pixel-based line toproduce a high rate selective laser melting process.

As described in more detail below, in some embodiments, output from theoptics assembly can be directed towards the powder layer using agalvo-scanner and then passed through a lens or lens assembly tominimize beam shape distortion for non-perpendicular incidence on thepowder layer such as an f-theta or telecentric lens.

In some embodiments, output of the optics assembly may be scanned in aprimary direction using a galvo-scanner while the entire optics assemblyis scanned in a secondary direction perpendicular to the primarydirection using a motorized stage actuator. Alternately the output ofthe optics assembly may be scanned in a fast motion using agalvo-scanner in a primary direction while the optics box is scanned ina slower motion in both the primary direction and a secondary directionperpendicular to the primary direction using orthogonally mountedmotorized stages. In other embodiments, the output from the opticassembly may be scanned using only motorized stage movement without anygalvo-scanner stage. In further embodiments, the optics assembly may bemounted such that the pixel array line output from the optics assemblyis oriented at a fixed angle relative to the motion stages such thatboth stages must be actuated to move the line perpendicular to the longaxis of the pixel line. Alternately this may be achieved with the outputfrom the optics assembly being scanned using a galvo-scanner. In otherembodiments, the output from the optics assembly may be dynamicallyrotated with respect to the motion stages during motion. Alternately thedynamic rotation of the optics box can be coupled with a galvo-scannerthat is fixed relative to the optics box.

In certain embodiments, the optics assembly may be mounted on amotorized stage that allows motion up and down perpendicular to a powderlayer on a build surface in conjunction with motorized motion in theother axes. This may allow for improved focusing of the output beams asthe beam is scanned back and forth with a galvo-scanner. Alternately,the optical path in the optics assembly can include an auto-focusingarray to enable fast dynamic focal length adjustment. This may allow forgreater focal length adjustment to accommodate a wider galvo-scanningrange.

Depending on the embodiment, a linear array of laser energy pixels(i.e., a line array) may have a uniform power density along the longlength of the line array. In some instances, the line output pixel arraycan have a non-uniform power density along the long length of the linearray by setting different power output levels for each pixel'sassociated laser energy source. Moreover, individual pixels on the endsof the linear array can be selectively turned off or on to produce aline array with a shorter length or longer length in the long direction.In some embodiments, all pixels except for a single pixel can beselectively turned off to obtain a single point pixel for fine featureprofiling. In certain embodiments, the linear array can be broken intomultiple smaller linear arrays in which the power density along eachsmaller linear array is the same. Alternately or additionally, themultiple smaller linear arrays can have different power densities thatare uniform in each smaller array but different from array to array. Insome instances, the multiple smaller linear arrays can have differentpower densities along each smaller array as well as different powerdensities between each small array.

Moreover, in some embodiments, the power levels of the various pixels ina linear array of laser energy may be independently controlledthroughout an additive manufacturing process. For example, the variouspixels may be selectively turned off, on, or operated at an intermediatepower level to provide a desired power density along the length of thelinear array.

According to some aspects of the current disclosure, the optical path ofthe incident laser beams after exiting the optical fibers may beimportant to obtain a uniform line shape on a powder surface. In someembodiments, an optical path of an additive manufacturing systemincludes a lens array including one or more micro-lenses (e.g., one ormore micro-lens arrays) followed by one or more objective lenses. Allbeams from the independent laser energy sources pass through the sameset of lenses in the lens array and the same objective lenses within anoptics assembly. As described in more detail below, the lens array(including the one or more micro-lenses) may be arranged to collimatethe laser energy output from each optical fiber source and transform thebeam shape from a round beam profile with a Gaussian power distributioninto a rectangular beam profile with a uniform power distribution inboth axes (e.g., a top-hat power distribution). In this manner, the lensarray may transform the laser energy output into an array of rectangularlaser energy pixels. The objective lens(es) may be arranged to define afocal length for the combined line array and serve to demagnify theoutput from the lens array. This demagnification changes the pixelspacing from the initial spacing, which is set by the distance betweenthe adjacent fibers in a fiber holder, down to a desired pixel spacingon the powder surface. For example, the objective lenses may be arrangedto demagnify the array such that there is no spacing between adjacentpixels.

According to some aspects, a laser line output from an optics assemblymay be a linear array comprising two or more rectangular pixels wherethe line is longer than it is wide when all of the pixels are in an onstate. For example, in a system with two laser energy sources, if bothlasers are being controlled to output the same laser power, then thepower density over the length of the line is substantially uniform.Alternately the power levels of these two pixels can be controlled to beat different levels resulting in a line output with varying powerdensity over the length of the line. In other embodiments, more than twopixels may be utilized to achieve a longer laser line. In some suchembodiments, the power density over the length of the line may be keptuniform by controlling each pixel to have the same power output.Alternately, any combination of power density along the line may beobtained by independently controlling the pixels to have different powerlevels.

The inventors have appreciated that the transformation of the beam shapeoutput from each laser energy source from a round Gaussian profile to asquare top hat profile is important to enable multiple track single passmelt pool stability on the powder surface. For example, FIG. 1 shows around beam with a Gaussian power density around its centerline. If tworound Gaussian beams are put adjacent to each other as shown in FIG. 2,the power densities combine depending on the exact beam powerdistribution. The combined power density on a line through the centersof both round profiles sums to that shown in the right graph in FIG. 2.The combined power density has defined peaks and valleys and is notuniform. If these two spots are moved in a direction orthogonal to theirstacked direction as shown in FIG. 3, then different tracks on thepowder surface will be exposed to different power profiles depending onthe position of the track relative to the incident beam's centerline.The track that is directly on the centerline of an individual round beam(track A in FIG. 3) will see a wider beam shape with a higher peakintensity compared to a track that is offset from the centerline of anindividual round beam (track B in FIG. 3). The most extreme differencefor different tracks will be between a track on an individual beamcenterline and a track at the point where two adjacent round beamsintersect. This difference in effective incident beam width and peakpower density for different tracks under the travelling line will resultin different melting rates and melt pool instabilities such as thosepreviously discussed.

In contrast to the round Gaussian beam shape discussed above, if theoutput from each independent laser energy source is shaped (e.g., usingone or more micro-lenses) into a rectangular beam shape with a uniformpower density (i.e., a top hat profile), then the resulting beam shapeand power density is that shown in FIG. 4. In both the X and Ydirections of the resulting rectangular beam shape, the power profile issubstantially uniform. If two rectangular profiles are then placedadjacent and moved orthogonally to their long stacked length, then thepower profiles of the adjacent beam profiles combined to provide asubstantially uniform profile both across the long length of the lineprojection as well as across the short width of the line. This meansthat each track line (tracks C, D and E in FIG. 5) sees the sameeffective beam width and peak power as all other tracks as the line isscanned over the powder surface.

Moreover, the inventors have appreciated that the uniformity of netpower exposure of the incident laser energy line on the powder surfaceis important to produce high quality fused material tracks. Asillustrated in FIGS. 6-9. a line consisting of multiple adjacentrectangular top hat profile pixels (FIGS. 6-7) produces a more uniformincident energy profile at all points in the scanned beam compared to asimilar line consisting of adjacent round Gaussian pixels (FIGS. 8-9).With the rectangular top hat profile, not only is the centerline powerdensity across the width of the line more uniform, but theoff-centerline power density across the width of the line is moreuniform. Even if a round Gaussian profile is converted to a round tophat profile (i.e., a round beam shape with a uniform power density),while the centerline power density profile between the rectangular andround beam shapes will be the same, the off centerline power density ofthe rectangular beam shape will be much more uniform than for the offcenterline power density of the top hat round beam shape. Accordingly,in all cases, a rectangular top hat beam shape for each pixel willproduce a more uniform power density at all points in a multi pixel linethan a similar multi pixel line that consists of either Gaussian or tophat profile round beam shapes. Moreover, a more uniform power densitymay produce less melt pool instability and may allow for greaterprocessing speeds, higher power densities and a wider process window.

According to some aspects, it may be important to operate an additivemanufacturing process with the powder surface positioned within thefocal point. For example, this may ensure the highest possible powerdensity as the incident beam area is minimized on the powder surface.This also may minimize the size of each pixel and allows for the highestpossible resolution of the resulting melt pool and fused part features.Operating outside the focal point may result in low effective powerdensities of the incident beam, which can result in requiring slowerscanning speeds and may slow net processing rates. Alternatively, higherpower laser energy sources may be required to operate at the same speedto obtain similar processing rates. These high net powers may cause meltpool instabilities, as discussed above, which would then also require alower processing speed to operate within a stable set of processparameters. Operating within the focal point also may aid in keeping thepower density profile across the width of the multi-pixel linesubstantially uniform. With operation outside of the focal point, thepixels may overlap and the power density profile across the length ofthe line may have undesirable peaks and valleys. Depending on theparticular embodiment, the type, number and spacing of the objectivelenses depends on the desired degree of demagnification, desired focallength and desired size of the focal point.

Another example of the impact of the power distribution in a lineararray of laser energy pixels is described with reference to FIGS. 10-13.Specifically, FIG. 10 depicts a linear array 200 that may be projectedonto a surface (e.g., onto a powder bed surface), and the linear arraycomprises a series of adjacent rectangular laser energy pixels 201-205.As discussed previously, the power density across the width of anindividual pixel can take on different distributions, and theinteraction of the power densities of the different distributions ofadjacent pixels will determine the uniformity of the power density ofthe linear array 200. If the power density distribution for anindividual pixel takes on a Gaussian form 210, then when multipleadjacent pixels are set to the same power level, the individuals pixels220, 221, 222 combine to form a single output line 230 with an outputpower density distribution that is the spatial sum of the individualpixels. The variation in density over this single output line 230 is dueto the variation within each pixel as well as the sum of the overlaparea between pixels. If the power density distribution for an individualpixel takes on a uniform distribution (i.e., a top hat form) 215, thenwhen adjacent pixels in the linear array 200 are set to the same powerlevel, the individual pixels 225, 226, 227 combine to form a singleoutput line 235. Since there is less variation across the width of eachindividual pixel and there is less overlap area between adjacent pixelscompared to the Gaussian pixels, the resulting output line 235 has amore uniform power density distribution compared to line 230 from theGaussian pixels. The same applies for power distribution across thewidth of the single output line. A top hat profile 215 across the widthof the pixels will result in a more uniform power density distributionthan for a Gaussian distribution 210 across the width.

As illustrated in FIG. 11, using a single output linear array 250 thatcomprises independently controllable laser energy pixels 251-255 hasadvantages compared to the use of individual fixed spot arrays 270 wherethe individual laser energy inputs have to be angled compared to eachother in order to accommodate the size of their optical arrays. In thesingle output linear array 250, individual pixels are all incident uponthe surface (e.g., a powder bed surface) at the same angle. This anglecan be normal to the surface (280) or at an acute angle to the surfaceeither away from the primary scan direction (281) or towards the primaryscan direction (282). All the pixels maintain the same angle at alltimes. For this case with a top hat power density profile across thewidth of the line, the power density for an acute angle (283, 284) has alower peak value but a wider width, depending on the actual incidentangle. In contrast, for a Gaussian distribution, the power densityacross the width of the line shows either an elongated lead-in 286 orelongated tail 288 with an acute incidence angle compared to a normalincidence pixel 287.

Moreover, with individual spot arrays 270, due to size limitations oftheir optical arrays, incident beams will always consist of combinationsof acute incident angles both towards (301) and away (302) from theprimary scan direction and may also include normal incidence spots(300). For individual spots with top hat power density distributions,this results in similar power distributions for spots with the sameincidence angles 303, 305, even from different directions, but differentpower densities for normal spots 304. For Gaussian power distributions,different incidence angles will result in some spots scanning with anelongated lead in 306 and an elongated tail 308 at the same time andpotential normal spot incidence without a lead in or tail 307. Thisprevents scan velocity optimization for the different incidence beams.As the incidence angle increases, the difficulty in managing thedifferent scan power density profiles increases.

FIG. 12 shows a line array with different possible outputs. The upperplot shows a potential array of 8 pixels that form a line. Each pixel inthis line can be set to the same power density to produce a full widthline with a uniform power density along the length of the line as shownin the upper most plot of FIG. 12. In some instances, individual pixelsmay be turned off to produce shorter individual lines as shown in themiddle plot of FIG. 12. Alternatively, the power level of each pixel canbe set individually to produce a line of almost any power density alongthe length of the line or along multiple smaller lines. As the totalline width increases and the pixel count increases, the ability to set anon-uniform power density along the length of the line can be useful foradapting the process to account for edge effects. Pixels on the powderbed surface that are adjacent on both sides to other pixels may requireless total incident power to obtain a stable melt pool condition thanpixels on the edge of a line. This is due to convective and conductivethermal losses at the edge of the line that have to be accommodated withmore power. Also, the presence or lack of fused material under anindividual pixel from the previous scan layer can affect the localthermal characteristics of the melt pool for a given pixel. One solutionto these edge effects and previous scan effects is to set a custom powerdensity across the length of the line depending on the boundaryconditions for that pixel at that point in the scan. The bottom plot inFIG. 12 illustrates a line power density with higher power at the twoedges and a stepped profile across the remaining pixels of the line.

FIG. 13 depicts another example of the ability to turn off individualpixels within a linear array. Similar to the arrangements discussedabove in relation to FIG. 12, this may allow for the use of differentlength line segments as well as multiple shorter segments. As shown inthe top plot of FIG. 13, a linear array can be divided down to theresolution of an individual pixel. By turning on or off individualpixels at various points during a scanning motion of an optics assembly,the ultimate resolution of a 3D feature formed from a powder bed fusionprocess is that of a single pixel. Line lengths can also be formed frommultiple pixels as shown in the middle two plots of FIG. 13 and down toa single pixel as shown in the bottom plot of FIG. 13. Single pixelresolution can be generated from any of the pixels in the linear array.In this way, fine resolution features at any point in the scanningmotion of the linear array can be generated by activating any singlepixel at any point. Single pixel resolution can also be obtained from asingle scan of a line array where the features are at an angle to thedirection of the scanned motion by turning on and off sequentialadjacent pixels at the optics unit is moved over the powder bed surface.

As described in more detail below, one or more objective lenses afterthe lens array including one or more micro-lenses may define a focallength and focal point of the combined beams (e.g., a linear array oflaser energy pixels). The focal length of the beams is the distance fromthe final objective lens of an optical assembly to a focal point. At thefocal point, each beam or pixel is at its minimum dimension and eachbeam is directly adjacent to a neighboring beam. For example, there maybe no spacing between adjacent beams such that the edges of adjacentlaser energy pixels are in contact with one another. This condition atthe focal point is schematically illustrated in FIG. 14. Away from thefocal point of the beams (in either direction along the beam path), thedimensions of the beams increase and the beams may start to overlap eachother as shown in FIG. 15. The focal point is typically defined as aregion along the beam path where the beam size is within a definedrange. In this example, it can be defined as a region in the beam pathwhere the rectangular profile dimension is less than a predeterminedvalue. In some instances. the focal point may be defined as a lengthalong the beam path and not an actual single point and is defined tostart when the size of an individual beam (e.g., a pixel dimension)decreases below a defined focus size and ends when the beam expands backabove the defined focus size.

In some instances, a rectangular top hat beam shape may be obtainedwithout the use of a lens array including micro-lenses. For example, ifa square optical fiber is used to deliver the power from the independentlaser energy sources, then the output from the fibers at the fiberholder is already in a square top hat shape with uniform power densityin both directions of the square. The independent outputs from thesquare optical fibers mounted in a fiber mount can be directed straightinto the objective lens stack for demagnification and focusing on thefiber surface.

However, the inventors have appreciated that the use of square fibersmay place additional requirements on the alignment and mounting of thefibers in the fiber mount. In particular, with a square fiber where thesquare top hat shape is established by the fiber itself, the fiber mountmust establish spacing and axial alignment, as well as rotationalalignment between the square shapes. If the square fibers are notrotationally aligned, the resulting pattern of pixels will be similarlymisaligned as illustrated in FIG. 16. In contrast, with round fibers anda lens array including one or more micro-lenses to shape the round beaminto rectangular beams as illustrated in FIGS. 17-18, the orientation ofthe fibers around their axis is not a critical parameter. Anyorientation of the round fibers is suitable as the ultimate rectangularshape of the pixels and orientation of the pixels is established andmaintained by the array of lenses. Since each micro-lens of the lensarray may be made as single monolithic part, maintaining alignmentbetween the rectangular beam shapes is inherent in the manufacturing ofeach lens and can be controlled. Accordingly, after the rectangularpixels pass through the objective lens(es), the output from the fiberoptical assembly will produce a uniform pixel array on the powdersurface without having to rotationally align the fibers.

Referring now to FIGS. 19-28, specific non-limiting embodiments ofadditive manufacturing systems according to the current disclosure aredescribed in further detail. It should be understood that the varioussystems, components, features, and methods described relative to theseembodiments may be used either individually and/or in any desiredcombination as the disclosure is not limited to only the specificembodiments described herein.

FIG. 19 depicts one embodiment of an additive manufacturing system 10.The system includes two or more independent laser energy sources 1coupled to associated optical fibers 2. For example, the independentlaser energy sources 1 may be Nd:Yag fiber lasers with maximum outputpowers of 10-2000 W. In some instances, the maximum output powers ofeach laser energy source may be 200-1000 W. In other embodiments, thelaser sources may include fiber coupled diode lasers. Each independentoptical fiber 2 for each independent laser energy source 1 is routed toan optics assembly 3, such that a first end of each optical fiber iscoupled to an associated energy source, and a second end of each opticalfiber is received in the optics assembly. As described in more detailbelow, the optics assembly 3 produces a combined optical output 6 whichis directed onto a powder bed surface 7 located on a build surface.

Each independent laser energy source 1 is connected to a central controlunit 4 using control cables 5. The central control unit 4 is configuredto independently control each laser energy source 1. For example, thecentral control unit may provide an on/off signal and a power outputsignal to each independent laser energy source. The power output signalto each independent laser energy source 1 can control the output powerfrom a minimum power level up to the maximum output power level of thelaser energy source. For example, the output power range may be from 10%to 100% of the maximum power output of each independent laser energysource 1.

FIG. 20 depicts one embodiment of an optics assembly 3. Within theoptics assembly 3, an end of each optical fiber 2 is received into afiber mount 20 (see FIG. 21). The fiber mount 20 fixes a spacing betweenadjacent optical fibers 2 and ensures that the axes of the opticalfibers 2 are parallel and aligned. On an output side of the fiber mount20, the ends of the optical fibers 2 are cut, cleaned and polished toensure a uniform and consistent beam exit from each individual opticalfiber 2. The combined laser output 34 from the individual optical fibers2 is directed towards a series of optical lenses 21-29. The combinedlaser output 34 forms a line from the adjacent independent laser sources1 projections through the individual optical fibers 2 that are linearlyarranged in the fiber mount 20.

As best illustrated in FIG. 21, when all the independent laser sources 1are on, the combined laser output 34 forms a continuous line 55comprising individual pixels 50-54. At this point along the optical pathwithin the optics assembly, the adjacent pixels 50-54 may overlap or thepixels may be separated from one another. The degree of overlap of thepixels 50-54 in the combined laser energy output 34 may depend on theoptical path that pixels 50-54 are passed through after the laser energyoutput exits the fibers 2 at the fiber mount 20. In this manner, anysuitable number of independent laser energy sources 1 can be coupledinto a single combined laser output 34. For example, in someembodiments, the number of independent laser energy sources 1 is in therange of 2-20, 5-50, or 10-100.

The combined laser output 34 within the optics assembly 3 is passedthrough a series of lenses 21-29. The number and type of lenses 21-29 isdependent on the desired output shape and focal length of the combinedoptical output 6 from the optics assembly. As illustrated in FIG. 22,the first lens 21 is a fast axis collimator followed by a slow axiscollimator 22, which are used to form the combined laser output 34 intoa line shape with a controlled overlap between adjacent pixels 60, 61,62 where each pixel is produced by the output of an independent laserenergy source 1. The fast axis collimator 21 and slow axis collimator 22are also used to modify the beam shape of each independent laser source1, for example to transform round beam profiles from the optical fibersinto rectangular laser energy pixels. The resulting pixel shapes 60, 61,62 still form a continuous output line 63 when all the independent lasersources 1 are turned on. This continuous output line 63 is then passedthrough an additional series of lenses 23-29 (see FIG. 20) that shapeand focus the output line within the optics assembly 3 to form acontrolled combined optical output 6.

The optics assembly 3 may contain mirrors 30, 31, 32 arranged to foldthe continuous output line of laser energy 63. In some cases, thisfolding helps to keeps the dimensions of the optics assembly 3 limited.In the depicted embodiment, the continuous output line 63 is folded twotimes in the optics assembly 3. However, it should be understood thatthe output line 63 may not be folded, may be folded once, three times,or any other suitable number of times as the current disclosure is notlimited in this regard. The optics assembly 3 further includes a frame36 that contains mounting and alignment features for the fiber mount 20,lenses 20-29 and mirrors 30-32. The optics assembly 3 also may includean adjustable focus array 37 with a set of adjustable lenses 27, 28, 29that can adjust the focal length of the combined optical output 6.

Depending on the particular embodiment, the combined optical output 6 ofthe optics assembly 3 may exit the assembly at any suitable orientation,such as at a right angle relative to the entry of the individual opticalfibers 2, parallel to the individual optical fibers 2, or at anarbitrary angle relative to the optical fibers 2.

FIG. 23 depicts another embodiment of an optics assembly 500. In thisembodiment, the independent optical fibers 600 enter on one side of theoptics assembly 500 and the ends 601 of the optical fibers are receivedby the fiber mount 602. The fiber mount ensures that the ends of theindividual fibers 601 are held securely and are aligned and parallelwithin the optical assembly. Depending on the particular embodiment. thespacing between individual fibers in the fiber mount may be betweenabout 500 microns and about 10 mm. For example, in some embodiments, thespacing between adjacent fibers may about 1 mm or about 2 mm. The endsof the individual fibers 601 are cleaved, ground and polished at theexit of the fiber mount 602. The beam outputs from the ends of theindividual fibers 601 are then directed at a cylindrical lens 603 thatcollimates the beams in a first direction normal to a plane that passesthrough the centers of the ends of the fibers 601. The beams then passthrough a cylindrical micro-lens array 604 that collimates the beams ina second direction orthogonal to the first direction. The beams thenpass through another cylindrical lens 605 that shapes the beams from around Gaussian to a rectangular top hat shape in the first direction.The beams then pass through a cylindrical micro lens array 606 thatshapes the beams from a round Gaussian to a rectangular top hat shape inthe second direction. Subsequently, the beams then pass throughcylindrical micro-lenses 607 and 608 that produces a Fouriertransformation in the first and second directions, respectively. At thispoint the beam can be folded using a mirror 610 or the beam can beallowed to continue in a straight path. The beams then pass through aset of spherical objective lenses 611-616 that demagnify the beams andset a focal length and focal point. The beam path may be folded by amirror 613 before, during or after passing through the objective lenses.The demagnification may be by a factor of 10:1 or 5:1 or 20:1 or anyrange thereof. The focal length may be set at 100 mm, 200 mm, 300 mm orany other suitable value by adjusting the objective lenses type andspacing. The exiting beam 620 from the final objective lens may bedirected straight towards the powder surface, or may be directed towardsthe powder surface using a mirror or scanning galvanometer controlledmirror.

Although cylindrical lenses and micro-lenses are described above tocollimate and shape the beam outputs, it should be understood that othertypes of lenses may be suitable. For example, in other embodiments, anysuitable combination of cylindrical lenses, spherical lenses, andconical lenses may be employed to collimate and/or shape the beamoutputs. Similarly, while spherical objective lenses have been describedabove, other lens shapes (e.g., cylindrical and/or conical lenses) maybe employed for the objective lenses. Accordingly, it should beunderstood that the current disclosure is not limited to any particularlens shapes or combination of lens shapes.

Referring now to FIG. 24, the combined optical output 6 may be directedtowards a mirror mounted on a galvanometer 80. In the depictedembodiment, the combined optical output 6 is turned towards the powderbed surface 7 by the galvanometer mounted mirror 80. As the galvanometermounted mirror 80 is rotated through an angle 84, the combined opticaloutput 81, 82 (after reflecting off of mirror 80) is scanned over adistance on the powder bed surface 7 defined by an angle 83. Theposition of the galvanometer mounted mirror 80 is driven by agalvanometer controller 85 which is in turn connected by an electricalcontrol cable 86 to the central control unit 4. The angle 83 throughwhich the combined optical output 81, 82 can be scanned is dependent onthe focal length of the combined optical output 6 from the opticsassembly 3. In some embodiments, the use of an adjustable focus array 37within the optics assembly 3 (see FIG. 16) enables a wider angle 83 forscanning the powder bed surface 7. In some instances, the optics box 3with the galvanometer mounted mirror assembly 80 can also be movedrelative to the powder bed surface 7, which may enable multiple modes ofscanning.

As depicted in FIG. 25, in some embodiments, the combined optical output6 from the optics assembly 3 may be directed towards the powder bedsurface 7 using a fixed mirror assembly 90 such that the optical output91 is fixed relative to the position of the optics assembly 3. Theoptics assembly 3 can then be moved relative to the powder bed surface 7to obtain a desired scanning pattern.

As discussed previously, the combined optical output from the opticsassembly that is directed towards the powder bed surface is in the formof a linear array of two or more adjacent rectangular laser energypixels formed from the output of the independent laser energy sources,and the linear array may be scanned over the powder bed surface toselectively melt a portion of the material on the powder bed to form adesired part.

FIG. 26 depicts a schematic representation of a linear array 110 on apowder bed surface 100 that includes a plurality of individual adjacentrectangular laser energy pixels 101-105. Depending on the particularembodiment, the laser energy pixels maybe shaped (e.g., via a lens arrayincluding one or more micro-lenses) to have any suitable size. Forexample, in some embodiments each rectangular pixel may have a width ofabout 50 microns to about 200 microns. In one embodiment, each pixel mayhave a width of about 100 microns. Moreover, the power level of eachindividual pixel 101-105 may be independently controlled by adjustingthe output of its respective independent laser energy source. Each pixel101-105 can also be independently turned on and off by controlling itsassociated laser energy source.

The resulting linear array 110 can be scanned over the powder bedsurface 100 in at least a primary direction 115 that is perpendicular tothe long dimension of the linear array 110 as well as in a secondarydirection 116 that is parallel to the long direction of the linear array110. For example, scanning in the primary direction 115 can be obtainedby moving the optics assembly or by scanning the combined optical outputfrom the optics assembly using a galvanometer mounted mirror assembly orother suitable arrangement. Moreover, in some instances, a combinationof moving the optics assembly while scanning with a galvanometer mountedmirror assembly can also be used to scan the combined optical outputover the powder bed surface in the primary direction. Scanning in thesecondary direction 116 can be obtained by moving the optics assemblyrelative to the powder bed surface 100. It should be understood thatsimultaneous scanning in both the primary and secondary directions canbe used to scan any desired pattern on the powder bed surface 100.

FIG. 27 depicts another embodiment in which an optics assembly 3 ismounted on a rotating stage that allows the optics assembly 3 to rotateabout an axis. This arrangement allows the linear array 110 to berotated on the powder bed surface 100 to a new position 111. In someinstances, this may allow for subsequent passes on the powder bedsurface to be made in different directions, which may cause the melttracks on subsequent layers 112, 113 to be rotated at an angle to eachother while enabling the full utilization of the line array in thescanning of both layers. For example, in some embodiments, the rotationangle of the optics assembly 3 between subsequent layers is betweenabout 30° and about 90° (e.g., about 30°, about 45°, or about 90°). Theaxis of rotation of the optics assembly 3 may be aligned with an axis130 passing through the center of the linear array 110. Alternatively,the axis of rotation of the optics assembly may be positioned away fromthe center of the linear array 110, such as along axis 131. In one suchembodiment, the position shift of the linear array 110 can be calculatedbased on the rotational axis displacement from the center of the lineararray 110. This offset can then be accommodated by applying an offset tothe primary and secondary scan positions. In some embodiments, theoptics assembly 3 can be simultaneously rotated while being moved in theprimary and secondary scan directions 115, 116 in order to obtain alinear array 110 of any desired orientation on the powder bed surface100.

FIG. 28 shows one possible layout for a multi-source powder bed laserfusion system. A build surface 510 can be indexed up or down using avertical slide system 560. A recoater head 570 is arranged to add alayer of material (e.g., a powdered metal) on to the build surface afterthe vertical slide is indexed down. An optics assembly 500 that receivesthe optical fibers from the multiple laser sources is mounted on anothervertical slide 550 that is mounted on a cross slide 540 that can producemotion in the lateral direction. Each end of the cross slide is mountedgantry style on linear slides 520,530 that enable the cross slide to bemoved in the other lateral dimension. In this manner, the output 501from the optics assembly may be scanned over the entire build surface asdesired.

While the present teachings have been described in conjunction withvarious embodiments and examples, it is not intended that the presentteachings be limited to such embodiments or examples. On the contrary,the present teachings encompass various alternatives, modifications, andequivalents, as will be appreciated by those of skill in the art.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. A method for additive manufacturing, the methodcomprising; shaping laser energy using at least one lens array includingone or more micro-lenses and one or more objective lenses positionedafter the at least one lens array to form a linear array of laser energypixels; exposing a layer of material on a build surface to the lineararray of laser energy pixels; and melting a portion of the layer ofmaterial due to exposure of the portion to the linear array of laserenergy pixels.
 2. The method of claim 1, further comprising controllinga power level of each laser energy pixel to adjust a power density alongthe linear array of laser energy pixels.
 3. The method of claim 1,further comprising moving the linear array of laser energy pixelsrelative to the build surface.
 4. The method of claim 3, wherein movingthe linear array of laser energy pixels comprises at least one oftranslating and rotating the linear array of laser energy pixels.
 5. Themethod of claim 1, wherein the linear array of laser energy pixels formsa homogenous line of laser energy on the build surface.
 6. The method ofclaim 1, wherein each laser energy pixel has a width between or equal toabout 50 micrometers and about 200 micrometers.
 7. The method of claim6, wherein each laser energy pixel has a width of about 100 micrometers.8. The method of claim 1, wherein each laser energy pixel has a squareshape.
 9. The method of claim 1, further comprising depositing a layerof material on the build surface with a material depositing system. 10.The method of claim 9, wherein the layer of material comprises a metalpowder, and depositing the layer of material comprises spreading themetal powder on the build surface.
 11. The method of claim 1, furthercomprising forming the linear array of laser energy pixels.
 12. Themethod of claim 11, wherein forming the linear array of laser energypixels comprises: transmitting laser energy from two or more laserenergy sources through two or more optical fibers, wherein each opticalfiber is coupled to one laser energy source at a first end of theoptical fiber; transmitting laser energy output from a second end ofeach optical fiber through the at least one lens array to transform thelaser energy output of each optical fiber from a round beam shape to arectangular beam shape having a uniform power density; and transmittingthe rectangular beams through the one or more objective lenses todemagnify the rectangular beams.
 13. The method of claim 1, wherein eachof the laser energy pixels comprises a rectangular laser energy pixel,and wherein each rectangular laser energy pixel has a substantiallyuniform power density.
 14. The method of claim 1, wherein each laserenergy pixel has a substantially uniform power density.
 15. The methodof claim 1, wherein there is no spacing between adjacent laser energypixels.
 16. A method for additive manufacturing, the method comprising;shaping laser energy using at least one lens array including one or moremicro-lenses and one or more objective lenses positioned after the atleast one lens array to form an array of laser energy pixels; exposing alayer of material on a build surface to the array of laser energypixels; and melting a portion of the layer of material due to exposureof the portion to the array of laser energy pixels.
 17. The method ofclaim 16, further comprising controlling a power level of each laserenergy pixel to adjust a power density along the array of laser energypixels.
 18. The method of claim 16, further comprising moving the arrayof laser energy pixels relative to the build surface.
 19. The method ofclaim 18, wherein moving the array of laser energy pixels comprises atleast one of translating and rotating the array of laser energy pixels.20. The method of claim 16, wherein the array of laser energy pixelsforms a homogenous line of laser energy on the build surface.
 21. Themethod of claim 16, wherein each laser energy pixel has a width betweenor equal to about 50 micrometers and about 200 micrometers.
 22. Themethod of claim 21, wherein each laser energy pixel has a width of about100 micrometers.
 23. The method of claim 16, wherein each laser energypixel has a square shape.
 24. The method of claim 16, further comprisingdepositing a layer of material on the build surface with a materialdepositing system.
 25. The method of claim 24, wherein the layer ofmaterial comprises a metal powder, and depositing the layer of materialcomprises spreading the metal powder on the build surface.
 26. Themethod of claim 16, further comprising forming the array of laser energypixels.
 27. The method of claim 26, wherein forming the array of laserenergy pixels comprises: transmitting laser energy from two or morelaser energy sources through two or more optical fibers, wherein eachoptical fiber is coupled to one laser energy source at a first end ofthe optical fiber; transmitting laser energy output from a second end ofeach optical fiber through the at least one lens array to transform thelaser energy output of each optical fiber from a round beam shape to arectangular beam shape having a uniform power density; and transmittingthe rectangular beams through the one or more objective lenses todemagnify the rectangular beams.
 28. The method of claim 16, whereineach of the laser energy pixels comprises a rectangular laser energypixel, and wherein each rectangular laser energy pixel has asubstantially uniform power density.
 29. The method of claim 16, whereineach laser energy pixel has a substantially uniform power density. 30.The method of claim 16, wherein there is no spacing between adjacentlaser energy pixels.
 31. The method of claim 16, wherein the array oflaser energy pixels comprises a rectangular array of laser energypixels.